JPH0313561Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) This invention aims to purify exhaust gas in a diesel engine by returning a portion of the exhaust gas to the intake system and recirculating it depending on the operating state of the engine. This invention relates to an exhaust recirculation control device for a diesel engine.

(Prior technology) As a measure to purify the exhaust gas of automobiles equipped with diesel engines,
The so-called exhaust gas recirculation (EGR), which returns a portion of exhaust gas to the intake system depending on the operating state of the engine, has been put into practical use with the main purpose of reducing NOx components. In a diesel engine, unlike a gasoline engine, the operating state of the engine is controlled by adjusting the amount of fuel pumped from a fuel pump to a fuel injection nozzle without controlling the amount of intake air. Therefore, the excess air that is not required for complete combustion of the fuel in the combustion chamber of the diesel engine depends on the amount of fuel injected during one intake stroke. Therefore, in a diesel engine with exhaust gas recirculation control, the amount of combustion injection is increased as the engine load increases, so when the engine is in a high-load operating range, the amount of exhaust gas recirculated is Control is performed to reduce the flow rate compared to when the engine is in a low-load or medium-load operating range, or to stop exhaust recirculation, thereby purifying exhaust gas and improving engine operating performance. Both will be achieved.

When a vehicle equipped with a diesel engine that performs exhaust gas recirculation as described above is driven at high altitudes, the amount of excess air decreases as the atmospheric pressure decreases at high altitudes, so the same control mode as at flatlands is used, for example.
If exhaust gas recirculation at high altitudes is performed using the same EGR rate (exhaust recirculation amount/exhaust recirculation amount + intake air amount) that corresponds to the engine operating conditions as at flatlands, more exhaust gas than necessary will be recirculated to the intake system. Sisters,
This results in the inconvenience of increased harmful components in the exhaust gas. For this reason, for example, as described in JP-A-57-157047, changes in atmospheric pressure are mechanically fed back, and as the atmospheric pressure decreases,
Exhaust recirculation control devices for diesel engines have been proposed to reduce the EGR rate.

The engine is equipped with a diesel engine exhaust recirculation control device that reduces the EGR rate at high altitudes compared to flatlands, thereby achieving both exhaust gas purification and improved engine performance at high altitudes. Even if the engine is in a low-load operating range, for example, when the amount of fuel injected is extremely small, such as when driving at a slow deceleration (for example, when the amount of access pedal depression exceeds the limit amount)
In cases where it is less than 5-10% (100%), there is little need for exhaust gas purification, and based on the idea of increasing oxygen concentration and improving combustibility, exhaust recirculation is stopped. Therefore, the exhaust gas recirculation is controlled by the exhaust gas recirculation means so that the EGR rate becomes zero.

When a vehicle equipped with such a diesel engine is driven at high altitudes, there is another problem other than the above-mentioned problem due to a decrease in atmospheric pressure. In other words, atmospheric pressure decreases as altitude rises above sea level, so the air that is sucked into the combustion chamber and compressed becomes colder as the altitude rises above sea level.
When the engine is in a low-load operating range, such as during gradual deceleration, the self-ignition properties of the mixed gas in the combustion chamber deteriorate, making misfires more likely to occur, reducing combustion stability and impairing engine performance. There is also a risk that unburned gas such as white smoke will be emitted.

(Purpose of the invention) In view of the above, the present invention returns and recirculates an amount of exhaust gas according to the operating state of the engine via an exhaust gas recirculation amount control means to purify the exhaust gas and improve engine operation. This is designed to achieve both improved performance and improve the self-ignition properties of the mixed gas in the combustion chamber when the engine is operating at low load at high altitudes, effectively reducing the occurrence of misfires. Another object of the present invention is to provide an exhaust recirculation control device for a diesel engine that can suppress the emission of unburned gas such as white smoke.

(Structure of the invention) The present invention has been made focusing on the fact that the temperature of compressed air in the combustion chamber can be increased by actively utilizing the heat retained in exhaust gas. The exhaust recirculation control device, whose basic configuration is shown in Fig. 1, controls the engine load value with respect to the exhaust recirculation means that returns and recirculates a part of the exhaust gas in the diesel engine to the intake system of the diesel engine. Exhaust recirculation region setting means for setting an operating region of the diesel engine corresponding to a predetermined range of as an exhaust recirculation region in which the exhaust recirculation means is operated;
When the value of atmospheric pressure detected based on the detection signal obtained from the pressure detection means for detecting atmospheric pressure becomes less than a predetermined value, the exhaust recirculation area set by the exhaust recirculation area setting means is changed to the corresponding exhaust recirculation area. and exhaust recirculation region changing means for changing the engine load value to a diesel engine operating region in which the value is reduced in accordance with the decrease in the atmospheric pressure value,
The operating state of the diesel engine, which is detected based on the detection signal obtained from the load detection means for detecting the engine load in the diesel engine, is determined by the exhaust recirculation region set by the exhaust recirculation region setting means or by the exhaust recirculation region changing means. An exhaust gas recirculation amount control means is provided and configured to change the amount of exhaust gas recirculated by the exhaust gas recirculation means in accordance with the operating state of the diesel engine detected at that time when the exhaust gas recirculation region is in the changed exhaust gas recirculation region. .

With this configuration, exhaust gas recirculation is carried out in accordance with normal engine operating conditions when the atmospheric pressure is normal, that is, on a flat ground, and when the atmospheric pressure decreases, that is, on a high ground. Exhaust gas recirculation is carried out even in low-load operating ranges where the engine load is small, such as during gentle deceleration driving, and as a result, the compressed air in the combustion chamber is warmed by the heat retained in the recirculated exhaust gas. The self-ignition property of the mixed gas in the combustion chamber is improved, and the occurrence of misfires is reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic configuration diagram showing an example of the exhaust recirculation control device for a diesel engine according to the present invention together with a diesel engine to which the device is applied. In FIG. 2, the diesel engine 1 is, for example, an in-line four-cylinder type swirl chamber type, and has four cylinders.
A branch portion of an intake passage 4 and an exhaust passage 5 is connected to each of the combustion chambers 2 . Each combustion chamber 2
As shown in FIG. 3, there is a main combustion chamber 11 surrounded by a cylinder block 6, a cylinder head 7, a piston 8, an intake valve 9 and an exhaust valve (not shown), and a nozzle hole 12 in this main combustion chamber 11. The cooling water temperature Ts related to the temperature state of the combustion chamber 2 is detected by a water temperature sensor SS mounted on the cylinder block 6. A chamber member 14 made of ceramic and fitted into a cavity provided in the cylinder head 7 is used on the peripheral wall of the swirl chamber 13, and this makes it possible to use a chamber member 14 made of ceramic that is fitted in a cavity provided in the cylinder head 7. It has a higher insulation effect than an engine, and is designed to burn faster. In this swirl chamber 13,
A heat generating portion 16a of a glow plug 16 for preheating and warm-up assistance attached to the cylinder head 7 faces out, and a combustion injection nozzle 17 is also provided. This fuel injection nozzle 17 injects a predetermined amount of fuel into the vortex chamber 1 according to the operating state of the diesel engine 1, which is pressure-fed from the fuel injection pump 18 every intake stroke.
It is designed to be injected into the

The fuel injection pump 18 is, for example, an electronically controlled distribution type injection pump, and has a drive shaft 19 that rotates synchronously with the diesel engine 1 by being given rotational driving force from the crankshaft of the diesel engine 1. A rotation speed sensor NS that detects the rotation speed of the rotary body in correlation with the rotation speed of the drive shaft 19 is arranged at a predetermined position. The fuel injection pump 18 also includes a governor device 2.
0 is provided, and the amount of fuel to be pumped to the fuel injection nozzle 17 is adjusted according to its operation. Furthermore, this fuel injection pump 18 has a built-in electronic timer 23 as a fuel injection timing adjustment means for advancing or retarding the injection timing of the fuel injected from the fuel injection nozzle 17 into the swirl chamber 13. The operation of the electronic timer 23 is controlled by an injection timing control valve 25. Further, an accelerator sensor AS is installed at the lever portion of the accelerator pedal 21 to detect an accelerator pedal depression amount Accp corresponding to the engine load Le.

The intake air introduced into the above-mentioned combustion chamber 2 from the intake passage 4 flows into the swirl chamber 13 during the compression stroke to form a swirl, mixes and burns the fuel injected there from the fuel injection nozzle 17, and then flows into the exhaust gas. A part of this exhaust gas is discharged into the exhaust passage 5 as a gas, but due to the difference in negative pressure between the intake passage 4 and the exhaust passage 5, a part of this exhaust gas flows into the exhaust gas whose both ends are connected to the intake passage 4 and the exhaust passage 5, respectively. The air is returned to the intake passage 4 through the reflux passage 30 to be refluxed. An exhaust gas recirculation control valve 31 is interposed in the middle of the exhaust gas recirculation passage 30 . The exhaust gas recirculation control valve 31 includes a partition wall 33 in which an exhaust gas recirculation port 32 is formed, which communicates the intake path 4 side and the exhaust gas path 5 side of the exhaust gas recirculation path 30, and a partition wall 33 that cooperates with the partition wall 33 to connect the exhaust gas recirculation port 32. The valve element 34 has a valve element 34 that opens and closes the valve, and a diaphragm mechanism 36 that drives the valve element 34 via a valve rod 35. The diaphragm mechanism 36 is configured to introduce negative pressure via a conduit 39 into a negative pressure introducing chamber 38 defined by a diaphragm 37 that connects and holds the valve rod 35. A coil spring 40 is compressed to apply a predetermined set load to 37. Further, a lift sensor RS that detects the lift amount of the valve element 34 and therefore the effective opening area of the exhaust gas recirculation port 32 is arranged in the diaphragm mechanism 36.

The negative pressure source side of the conduit 39 that introduces negative pressure into the negative pressure introduction chamber 38 is connected to the negative pressure supply port 42 of the negative pressure control valve 41, and the vacuum port 43 of the negative pressure control valve 41 is connected, for example, to the negative pressure supply port 42 of the negative pressure control valve 41. , is connected via a conduit 45 to a vacuum pump 44 which is rotationally driven by a crankshaft (not shown) of the diesel engine 1. In addition to the negative pressure supply port 42 and vacuum port 43, the negative pressure control valve 41 has an atmospheric suction port 46 that communicates with the atmosphere, and as shown in FIG.
When both the solenoid 47 on the side and the solenoid 48 on the vacuum port 43 side are not energized and excited, the valve elements 49 and 50 are pressed down by the elasticity of the spring members 51 and 52, and the negative pressure supply port 42 and the atmosphere intake port 46, and the vacuum port 43 is closed. Conversely, when both the solenoid 47 and the solenoid 48 are energized, the valve elements 49 and 50 are in communication with each other. is pulled up against the elasticity of the spring members 51 and 52, so that the negative pressure supply port 42 communicates with the vacuum port 43.

In order to control the operation of each part configured as described above, a control unit 100 having a built-in timer is provided, and this control unit 100 includes the following:
A detection signal Ss corresponding to the cooling water temperature Ts related to the heating state of the diesel engine 1 from the water temperature sensor SS, a detection signal Sn corresponding to the rotation speed Ne of the diesel engine 1 from the rotation speed sensor NS, and an accelerator sensor AS Amount of accelerator pedal depression from
Accp, therefore, a detection signal Sa corresponding to the engine load Le, and a detection signal Sr corresponding to the effective opening area of the exhaust recirculation port 32 from the lift sensor RS, and therefore the amount of exhaust gas recirculation are input, respectively; Further, a detection signal Sb corresponding to a change in the primary voltage from the battery BS, a detection signal Sd corresponding to the atmospheric pressure Ps from the atmospheric pressure sensor DS, etc. are input.

The control unit 100 then controls the injection timing control signal Ct, which controls the fuel injection timing of the diesel engine 1, based on the various detection signals Ss, Sn, Sa, Sr, Sb, Sd, etc. described above. An exhaust recirculation control signal Ce for controlling the amount of recirculation of exhaust gas is applied to the valve 25, and an exhaust recirculation control signal Ce is applied to the negative pressure control valve 41.
Heating control signal for heating the glow plug 16 and the glow register 59 provided in the intake passage 4
Send Cg.

Under the control of the control unit 100 which sends out the control signals Ce, Ct, and Cg as described above, exhaust gas recirculation control in an example of the exhaust gas recirculation control device for a diesel engine according to the present invention is performed as described below.

The control signal Ce sent from the control unit 100 to the negative pressure control valve 41 is a pulse signal having a pulse width _t1 and a period t depending on the operating state of the diesel engine 1, as shown in FIG.
When exhaust gas recirculation control is implemented (during EGR control)
When the solenoid 47 and the solenoid 48 of the negative pressure control valve 41 are energized every unit cycle t with a pulse width t ₁ according to the operating state of the diesel engine 1, and when exhaust recirculation control is not performed (when EGR is stopped) In this case, the pulse width t ₁ of the control signal Ce is set to zero.

In addition, in this example, the region where exhaust gas recirculation is performed (EGR region) is the accelerator pedal depression amount Accp
and the engine rotation speed Ne, for example, the detection signal Sd obtained from the atmospheric pressure sensor DS.
When the atmospheric pressure detected based on the normal atmospheric pressure is normal, therefore, on flat ground, the accelerator pedal depression amount Accp is indicated by Z, as shown by the diagonal line surrounded by the solid line in Fig. 6. range from ₁ to _e2 ,
For example, the engine speed Ne is in the range of about 7 to 60%, assuming the limit amount of depression is 100%, and the engine speed Ne is, for example,
Exhaust gas recirculation is performed only in the range of 600 to 3000 rpm, and is not performed when the diesel engine 1 is in a high load operating range or when the engine load is relatively small.

When the exhaust gas recirculation control is performed using the control signal Ce, the control signal Ce, which is a pulse signal having a pulse width _t1 and a period t according to the operating state of the diesel engine 1, is sent from the control unit 100 to the negative pressure. It is supplied to the control valve 41. As a result, the negative pressure supply port 42 of the negative pressure control valve 41 is connected to the vacuum port 43 and the atmospheric suction port 4.
6, the duty of the control signal Ce (t ₁ /
t), and therefore, the negative pressure in the negative pressure introduction chamber 38 of the diaphragm mechanism 36 in the exhaust recirculation control valve 31 is controlled by the control signal.
As the duty (t ₁ /t) of Ce increases, its absolute value increases, and accordingly, the effective opening area of the exhaust gas recirculation port 32 obtained when the diaphragm 37 is pulled up against the elasticity of the coil spring 40 increases. is increased, and the amount of exhaust gas recirculation is increased.

On the other hand, when the pulse width t ₁ of the control signal Ce is zero and the exhaust gas recirculation control is not performed, the communication between the negative pressure supply port 42 and the vacuum port 43 is cut off, and the communication between the negative pressure supply port 42 and the atmospheric air intake is interrupted. The absolute value of the negative pressure in the negative pressure introducing chamber 38 is reduced, the diaphragm 37 is pushed down by the elasticity of the coil spring 40, the exhaust gas recirculation port 32 is closed, and the exhaust gas recirculation is stopped.

On the other hand, the detection signal obtained from the atmospheric pressure sensor DS
When the atmospheric pressure detected based on Sd is lower than the normal atmospheric pressure and is below a predetermined value,
Therefore, at high altitudes, the EGR region is smaller than the above-mentioned EGR region at flatlands, as shown by the broken line in FIG. The lower limit value of the EGR region decreases from e ₁ to e′ ₁ in Fig. 6 with respect to the accelerator pedal depression amount Accp. The upper limit was changed from e ₂ to e′ ₂ , and the range indicated by Z′ in Fig. 6 was changed.
Considered to be the EGR area. As a result, exhaust gas recirculation will be performed even when the engine is in a low-load operating range, such as when the engine load is relatively small, such as during gentle deceleration, where exhaust gas recirculation would not have been performed in the past. Furthermore, conventionally, exhaust gas recirculation is performed, but when the engine is in a high load operating range, exhaust gas recirculation is stopped. and,
With the EGR region shifted to the low engine load side as described above, the control unit 100 performs exhaust recirculation control using the control signal Ce, similar to the case on the flat ground described above.

In this way, the EGR region is shifted to the low engine load side in response to a decrease in atmospheric pressure, so for example,
Even when the amount of fuel injected is extremely small, such as when driving at a slow deceleration at high altitudes, exhaust gas recirculation is carried out, and the air sucked into the combustion chamber 2 is warmed by the heat retained in the recirculated exhaust gas. The temperature of the compressed air in the combustion chamber 2 is increased, so that the self-ignition performance of the mixed gas in the combustion chamber 2 is improved even when the diesel engine 1 is in a low-load operating range. Furthermore, when the diesel engine 1 is in a high-load operating range at high altitudes where the air is thinner than at flatlands, where the amount of fuel injection is increased and the amount of excess air is even smaller, exhaust recirculation is stopped. , sufficient combustion air is taken in to improve combustibility.

Control unit 100 that operates as described above
is configured using, for example, a microcomputer, and describes an example of a program for exhaust gas recirculation control executed by the central processing unit (CPU) of the microcomputer in such a case with reference to the flowchart in FIG. do.

In this program, after starting, first in process 101, the atmospheric pressure Ps obtained from the atmospheric pressure sensor DS, the engine rotation speed Ne obtained from the rotation speed sensor NS, the accelerator pedal depression amount Accp obtained from the access sensor AS, etc. Performs operating state detection to capture data. Continued decision 1
At 02, the atmospheric pressure Ps from the atmospheric pressure sensor DS
Based on the data, it is determined whether the pressure is normal atmospheric pressure or not. As a result of this determination, if it is determined that the pressure is normal, that is, the area is on a flat surface, the process proceeds to decision 104, where it is determined whether or not the area is in the EGR region. For this judgment, as shown in Fig. 6 mentioned above, the vertical axis is the accelerator pedal depression amount Accp, and the horizontal axis is the engine rotation speed Ne. An EGR region map is used in which the EGR region is a region in which the depression amount Accp is in the range of 7 to 60% when the limit depression amount is 100%, and the engine rotation speed Ne is in the range of 600 to 3000 rpm. Then, by comparing this EGR region map with the data of the accelerator pedal depression amount Accp and the engine rotation speed Ne taken in process 101, it is determined that the accelerator pedal depression amount Accp and the engine rotation speed Ne are in the above-mentioned EGR region. If it is within
Then, a control signal Ce, which is a pulse signal having a pulse width t ₁ and a period t depending on the operating state of the engine, is formed and sent to the negative pressure control valve 41 . As a result, the exhaust gas recirculation port 32 is opened and closed according to the duty (t ₁ /t) of the control signal Ce, and exhaust gas recirculation control is performed in which a predetermined amount of exhaust gas is returned to the intake system and recirculated. And then process 101
Return to

In addition, in decision 104, if it is determined that the accelerator pedal depression amount Accp and the engine speed Ne are outside the above-mentioned EGR range, then it is assumed that the engine is in the low-load operation range where the engine load is low or the engine is in the high-load operation range. Since it is desirable to cut off the recirculation of exhaust gas and allow a large amount of air with high oxygen concentration to be drawn into the combustion chamber 2, the process proceeds to process 106 in order to stop the recirculation of exhaust gas. Then, in process 106, the control signal with the pulse width t ₁ set to zero is
Ce is delivered to the negative pressure control valve 41 and the process returns to process 101.

On the other hand, if the decision 102 determines that the atmospheric pressure is lower than normal and below a predetermined value, and therefore it is determined that the location is at a high altitude, the process proceeds to process 103, and the process shown in FIG. The EGR region surrounded by the solid line shown is shifted by d (%) in the direction in which the accelerator pedal depression amount Accp becomes smaller, that is, toward the low engine load side, as the atmospheric pressure decreases from a predetermined value, By lowering the lower and upper limits of the accelerator pedal depression amount Accp that define the EGR region, the region surrounded by the broken line shown in FIG. 6 is defined as the EGR region, and the decision 104
Proceed to. In decision 104, the EGR area map showing the migrated EGR area and the amount of accelerator pedal depression captured in process 101 are displayed.
The data of Accp and the data of engine rotational speed Ne are compared, and if the accelerator pedal depression amount Accp and the engine rotational speed Ne are within the above-mentioned shifted EGR region, the process proceeds to process 105. Then, in process 105, as in the case of the flat ground described above, a control signal Ce, which is a pulse signal having a pulse width _t1 and a period t according to the operating state of the engine, is sent to the negative pressure control valve 41, and the exhaust gas is Reflux control is performed. Then, the process returns to process 101. In addition, if the accelerator pedal depression amount Accp and engine speed Ne are outside the EGR range shifted to the low engine load side in decision 104, the recirculation of exhaust gas is cut off and air with high oxygen concentration is supplied to the combustion chamber 2. Since it is preferable to inhale the exhaust gas, the process proceeds to step 106 to stop the exhaust gas recirculation.
The control signal Ce with t ₁ set to zero is sent to the negative pressure control valve 41, and then the process 101
Return to

(Effects of the invention) As is clear from the above explanation, according to the exhaust recirculation control device for a diesel engine according to the present invention,
The exhaust gas is returned to the intake system and recirculated according to the operating state of the engine, thereby achieving both purification of the exhaust gas and improvement of engine operating performance, and
When a vehicle equipped with this exhaust recirculation control device for a diesel engine is running at high altitudes, the lower limit value for the engine load in the region where exhaust recirculation should be performed is lowered in response to a decrease in atmospheric pressure, and thereby, Exhaust gas recirculation is carried out even when the engine is in the low-load operating range, and then the intake air is warmed by the heat retained in the exhaust gas, increasing the compressed air temperature and reducing the self-ignition property of the mixed gas in the combustion chamber. considered to be good.

Therefore, in a car equipped with the diesel engine exhaust recirculation control device according to the present invention, misfires in the engine can be effectively prevented even when the amount of fuel injection is extremely small, such as when driving at high altitudes and at deceleration. As a result, operational performance is improved, and emissions of unburned gas such as white smoke are reduced.

In addition, as in the above-mentioned embodiment, when driving at high altitudes, the lower limit value for the engine load in the area where exhaust gas recirculation should be performed is lowered and the upper limit value is also lowered in accordance with the decrease in atmospheric pressure, and the exhaust gas recirculation is performed. If the entire area where the engine load is required is shifted to the low engine load side, exhaust recirculation will be stopped at high altitudes in some areas on the high engine load side, where exhaust recirculation is carried out on level ground. As a result, a sufficient amount of intake air can be obtained when the engine is in a high-load operating range, so that the operating performance of the engine can be improved.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram showing an exhaust recirculation control device for a diesel engine according to the present invention in accordance with the scope of the utility model registration claim, and Fig. 2 shows an example of the exhaust recirculation control device for a diesel engine according to the present invention. 3 is a partial sectional view of the main body of the diesel engine shown in FIG. 2, and FIG. 4 is a sectional view of the negative pressure control valve shown in FIG. Figures 5 and 6
The figure is a waveform diagram and characteristic diagram used to explain the operation of the example shown in FIG. 2, and FIG. It is. In the diagram, 1 is a diesel engine, 2 is a combustion chamber,
4 is an intake passage, 5 is an exhaust passage, 30 is an exhaust recirculation passage, 31 is an exhaust recirculation control valve, 32 is an exhaust recirculation port, 36 is a diaphragm mechanism, 41 is a negative pressure control valve, 100 is a control unit, and DS is atmospheric pressure. Sensors: AS is the accelerator sensor, NS is the rotation speed sensor, and RS is the lift sensor.

Claims (1)

[Claims for Utility Model Registration] Exhaust recirculation means for returning a portion of exhaust gas in a diesel engine to the intake system of the diesel engine for recirculation; Exhaust recirculation area setting means for setting an exhaust recirculation area in which the exhaust recirculation means is operated; pressure detection means for detecting atmospheric pressure; and atmospheric pressure detected based on a detection signal obtained from the pressure detection means. When the value of becomes equal to or less than a predetermined value, the exhaust recirculation region set by the exhaust recirculation region setting means is reduced in accordance with the decrease in the value of the atmospheric pressure. Exhaust recirculation region changing means for changing the operating region to an operating region; Load detecting means for detecting engine load in the diesel engine; and Operating state of the diesel engine detected based on a detection signal obtained from the load detecting means. is in the exhaust gas recirculation area set by the exhaust gas recirculation area setting means or in the exhaust gas recirculation area changed by the exhaust gas recirculation area changing means, the amount of exhaust gas recirculated by the exhaust gas recirculation means is determined by the load detection. An exhaust gas recirculation control device for a diesel engine, comprising: an exhaust gas recirculation amount control device that changes the amount of exhaust gas recirculation according to an operating state of the diesel engine detected based on a detection signal obtained from the device.